A vehicle is subjected to vibration while it is moving. The vibration is transmitted to the seat, which is uncomfortable and inconvenient for passengers. This applies in particular to aircraft or the like, such as a helicopter, in which the vibration generated by the displacement of the vehicle is at a high frequency, such as, for example, a frequency lying in the range 10 hertz (Hz) to 25 Hz, approximately, at an amplitude that is small compared with the movements commonly induced for the passenger because of the progress of the vehicle.
As a result, a general problem that arises in the field lies in finding arrangements for seats to absorb such vibration in such a manner as to avoid transmitting them to passengers.
Proposals have been made for arrangements for the seats proper of seats in order to damp the movements induced for passengers during progress of the vehicle. Such seats proper are secured to the chassis of the vehicle and are organized as flexible elements, e.g. being constituted by a block of foam or a lattice of straps under tension.
It is found that such arrangements do not provide satisfactory stability as is desired for a passenger, in particular along the passenger's gravity axis. Furthermore, such arrangements are unsuitable for absorbing vibration of the type mentioned above, in particular for a vehicle of the aircraft type.
Proposals have also been made to interpose elastically deformable means between the seat and the chassis of the vehicle, or between a seat proper and a framework carrying it, in order to damp the jolts that are caused by progress of the vehicle. Nevertheless, such damper means are found to present the drawback of being too flexible, and unsuitable for absorbing vibration of the above-mentioned type, at least not without significantly and unacceptably increasing the weight and/or the size thereof in order to stiffen their flexibility. It should be observed that any such increase in weight and size is particularly unsuitable for use in aircraft. Furthermore, since passengers are likely to present significant differences in corpulence, such arrangements whose effectiveness depends on the weight that the damper means are able to support, are themselves unsuited for performing their desired function of absorbing vibration, when faced with the potential for seats to be used by passengers presenting a variety of previously unidentified sizes.
Proposals have also been made for seats in which the seat proper is supported by a vehicle structure via co-operating means to enable the seat proper to slide relative to the vehicle structure, where such means may be wheels or the like traveling in slideways. A drawback of arrangements of that type lies in the unacceptable friction between the co-operating members leading to specific forces preventing the seat proper from moving relative to the vehicle structure, and thus countering the looked-for effect of absorbing vibration. Furthermore, another drawback lies in the mechanical relationship involved between the co-operating members and the stresses that result against them, thereby leading to unsuitable jolts being produced.
Finally, it is found that the difficulties to be overcome in the field lie in particular in arranging a seat for a vehicle that is suitable for absorbing vibration at relatively high frequency while not being of very large amplitude, in the face of the movements that are commonly induced on the passenger because of the progress of the vehicle and because of the directional movements thereof. In particular, such an arrangement must enable said vibration to be absorbed in the general plane of the seat proper, but without thereby transmitting jolts or instability to the passenger along the passenger's gravity axis in particular. Furthermore, such an arrangement must provide such a facility for absorbing vibration in spite of supporting passengers of previously unidentified corpulence that can lie in a relatively large range. In addition, in particular for implementation in an aircraft or the like, such an arrangement must present size and weight that are as small as possible, and must do so at a cost that is acceptable.